The present invention relates to an information recording method, by which write information is converted into a series of codes according to the run length limited coding rule and the series of codes is recorded while making it correspond to the positions of the lead edge and the tail edge of record marks formed in a data area on a recording medium and to an information storing apparatus using same. In particular, the present invention relates to an information recording method efficient for reducing level fluctuations of a signal reproduced in the case where data coded by using a coding rule having no DC free property are recorded on an optical disk medium and to an optical disk apparatus using same.
In an optical disk memory device, improvement in the signal-to-noise ratio of a reproduced signal and increase in the data detection window margin are effective for improving the reliability of data, i.e. reducing the error ratio. Two methods are known for converting a reproduced signal into a binary signal. By a first method a detection signal obtained from a record mark recorded on an optical disk is converted into a binary signal by using a certain slice level (hereinbelow denoted by original waveform detection method, but called also amplitude detection method), while by a second method a position corresponding to a code is detected by differentiating the detection signal (hereinbelow denoted by differentiation detection method, but called also peak detection method).
By a method, by which a code is made correspond to the center of the record mark, generally the detection signal from an optical head is first-order-differentiated and a zero cross point of a first-order-differentiation signal thus obtained is detected (hereinbelow denoted by mark position recording method). Further by a method, by which the code is made correspond to the two edges of the record mark (hereinbelow denoted by mark length recording method), generally the detection signal from an optical head is second-order-differentiated and a zero cross point of a second-order-differentiation signal thus obtained is detected.
The decrease in the signal-to-noise ratio produced when the reproduced signal is converted into the binary signal is smaller by the original waveform detection method. In the case of the differentiation detection method, since a frequency band is increased in the neighborhood of a differentiation constant (cut-off frequency), it is necessary to secure an originally satisfactorily good signal-to-noise ratio.
On an optical disk, apart from user data, specified data such as address data indicating the position on the disk, a pattern for pulling-in a PLL (Phase Locked Loop) for generating a reproduction clock, resynchronizing patterns inserted with a certain interval according to a predetermined format, etc. are recorded. Generally the address information is previously built-in in the form of pits at the fabrication of the disk. An example of such a format is determined by an ISO norm for a disk of continuous servo system having a diameter of 130 mm.
Here explanation will be made, taking this ISO norm as an example. For the coding system the mark position recording system using 2-7 RLL (Run Length Limited) coding is adopted and a one-byte resynchronizing mark is inserted for every 20 bytes of data. The resynchronizing mark (RESYNC) has a function of correcting the synchronization, in the case where the phase relation between the reproduction clock generated by the PLL and reproduced data is deviated by 1 bit or more because of defects, etc. on the disk. The number of data bytes between two adjacent resynchronizing marks is set within an extent, where errors can be corrected by the ECC (Error Correction Code). For this ISO format, since the mark position recording system is used and the position of the mark is detected by the differentiation detection method, no DC free property is required. Further only one sort of resynchronizing marks is used and no change thereof depending on the data pattern is effected.